Altitude Calculator
Estimate air pressure, temperature, and oxygen availability at any altitude, using the International Standard Atmosphere model.
What this calculator does
Estimates air pressure, temperature, and oxygen availability at any altitude using the standard atmosphere model, useful for travel planning, cooking adjustments, or general curiosity about conditions at elevation.
Who this is for
Travelers and hikers planning a trip to elevation, anyone adjusting a recipe for high-altitude cooking, or people curious about why breathing and boiling water both work differently in the mountains.
How this calculator works
Uses the International Standard Atmosphere (ISA) model for the troposphere (0–11,000m): pressure decreases following the barometric formula P(h) = P₀ × (1 − L×h/T₀)gM/RL, where L is the standard temperature lapse rate (6.5°C per 1,000m), and temperature decreases linearly at that same lapse rate. Oxygen availability is shown as the percentage of sea-level oxygen molecules present per breath — not a change in the 20.9% atmospheric composition, but a drop in total air density.
Worked example
At 2,500m with a 15°C sea-level temperature: temperature drops by the lapse rate (6.5°C per 1,000m × 2.5 = 16.25°C), giving a local temperature of roughly −1.25°C. Air pressure falls to approximately 74% of sea-level pressure at this altitude, meaning each breath draws in correspondingly fewer oxygen molecules — this is right around the altitude (2,400-2,500m) where many people first begin noticing symptoms of reduced oxygen availability.
Common mistakes
- Assuming the air has less oxygen "in it" at altitude. Oxygen stays at ~20.9% of the atmosphere by volume at any inhabited altitude — what actually drops is total air pressure, meaning fewer air molecules (and therefore fewer oxygen molecules) enter your lungs per breath.
- Using sea-level boiling/cooking times unchanged at altitude. Water boils at a lower temperature as pressure drops (roughly 1°C lower per 300m), which is why high-altitude cooking often needs longer times or adjusted recipes.
- Ignoring acclimatization time. The pressure and oxygen figures here are instantaneous physical facts, not a prediction of how your body will feel — altitude sickness risk depends heavily on ascent speed and individual acclimatization, not just the altitude number itself.
- Applying the troposphere formula above 11,000m. Above that altitude, a different atmospheric layer model applies with a different (near-constant) temperature profile — this calculator's formula is only accurate up to the troposphere boundary.
Related calculators
Frequently Asked Questions
Why does water boil at a lower temperature at altitude?
Boiling happens when a liquid's vapor pressure equals the surrounding air pressure. Since air pressure drops at altitude, water needs less heat energy to reach that point — roughly 1°C lower boiling point for every 300m of elevation gain, which is why high-altitude recipes often need longer cooking times.
Does the percentage of oxygen in the air change with altitude?
No, oxygen stays at about 20.9% of the atmosphere by volume up to very high altitudes. What changes is the total air pressure, so each breath contains fewer oxygen molecules overall — that's why altitude sickness happens, not because the air composition changes.
At what altitude do people typically start feeling altitude sickness?
Symptoms can begin around 2,400–2,500 meters (8,000 feet) for many people, where air pressure has dropped to roughly 75% of sea level. Susceptibility varies significantly by individual and acclimatization.
Is this formula accurate at very high altitudes like Mount Everest?
This calculator uses the standard troposphere model, accurate up to about 11,000 meters (36,000 feet) — which covers Mount Everest's summit (8,849m) and all commercial aircraft cruising altitudes. Above 11km, a different atmospheric layer model applies.